Representative patented prior art relating to bag machines and bag machines incorporating devices for producing stacks of counted bags include U.S. Pat. Nos. 3,580,142 to Stock, Re. 27,523 to Maccherone and 3,663,338 to Wech, all of which are assigned to the assignee of the present application.
A variety of conditions resulting from the physical properties of thermoplastic web material hinder developing a stack of bags whose corresponding edges overlie each other to thereby create a stack much like a deck of cards. One condition whose magnitude depends upon the type of thermoplastic material is static. Converted web segments, by virtue of their manipulation by the machine elements themselves develop indiscriminate areas of positive and negative charges hindering proper stacking. The conventional approach to eliminating such static charges involves the utilization of high frequency AC static eliminator bars that create an AC field neutralizing the static charge on the web elements. Avoiding use of static eliminators is desirable as to initial cost and maintenance.
Thermoplastic web material of the type referred to as "low density polyethylene" (hereinafter sometimes referred to as LDP) has greater strength and is stiffer than low density polyethylene. Accordingly, low density polyethylene can be made much thinner with the result, however, it is much more difficult to stack bags or other web segments made therefrom. Moreover, low density polyethylene is very slippery therefor requiring firm control of a stack of bags during production, packing and dispensing at the retail level.
Stacking mechanisms associated with bag machines for producing side weld or bottom weld bags have been reasonably successful in those instances where the size of the bag is small. A small bag in the terms of reference used herein means a bag whose length and width are substantially equal and are from 30 to 50 square inches in area. Stacking was achieved by propelling the bag to a collection tray or an area defined by fences on a stacking table. Low density polyethylene produces stacks which are soft and fluffy due to trapped layers of air between the individual bags and therefore greatly decreasing stack density which, in some cases, limits the number of bags which can be accumulated in a stack. Stackers also include pins on which the bags are impaled in register. This approach is objectionable due to the holes created by the pins.
Prior art solving the problem of generating and maintaining a registered stack of bags regardless of the type of thermoplastic film being used or bag size is shown and described in U.S. Pat. No. 3,587,410 to Dechanciaux, U.S. Pat. No. 4,083,747 to Rochla and U.S. Pat. No. 3,748,973 to Kuck. The first mentioned patent discloses a clamping arrangement operative to clamp the web segment fed by the machine before it is cut and sealed and maintains a clamping pressure on the bag stack during the time when another web segment is fed. U.S. Pat. No. 4,083,747 provides a seal bar perforating arrangement for separating the web into segments defined by laterally spaced seals having a line of perforation therebetween. Bags are created by providing sequentially operable clamping mechanisms that separate web segments to define the individual bags and the bags are collected in a registered pile. U.S. Pat. No. 3,748,973 discloses collecting bags in gripping units being operable to transfer successive stacks from a cylinder to a table. German Pat. No. 1 206 295 discloses transfer of bag stacks on a stacking table.